The first developer build of OS X 10.8.2 arrives as Build 12C31a in the form of a 641.83 MB combo update, and Apple is asking testers to focus on Messages, Facebook, Game Center, Safari, and Reminders. Apple also notes no known issues with the build, and we'll provide additional information on the update as it surfaces.

sorry i should have explained when i posted that apple hadn't yet updated the mac dev center frontpage and initially to access it you had to click on the "View all downloads" link at the bottom of the page.

Release notes included in the installer. Notice the mention of iOS 6 and Passbook:

The 10.8.2 update is recommended for all OS X Mountain Lion users and includes new features and fixes. New features include:

Facebook
• Single sign on for Facebook
• Facebook as an option when sharing links and photos
• Facebook friends' contact information and profile pictures in Contacts
• Facebook notifications in Notification Center

Game Center
• Share scores to Facebook, Twitter, Mail, or Messages
• Facebook friends are included in Game Center friend recommendations
• Facebook Like button for games
• Challenge friends to beat your score or achievement

Other new features
• Power Nap support for MacBook Air (Late 2010)
• iMessages sent to your phone number now appear in Messages on your Mac
• From Safari and Mail on your Mac you can add passes to Passbook on your iPhone or iPod touch running iOS 6
• New shared Reminders lists
• FaceTime now receives calls sent to your phone number
• New sort options allow you to sort notes by title, the date you edited them, and when you created them
• Dictation now supports Mandarin, Cantonese, Spanish, Korean, Canadian English, Canadian French, and Italian
• The Dictionary application now includes a French definition dictionary
• Sina Weibo profile photos can now be added to Contacts

The 10.8.2 update also includes general operating system fixes that improve the stability, compatibility and security of your Mac, including the following fixes:
• An option to discard the changes in the original document when choosing Save As
• Unsent drafts are opened automatically when launching Mail
• Receive Twitter notifications for mentions and replies from anyone
• URLs are shortened when sending tweets from Notification Center
• Notifications are disabled when AirPlay Mirroring is being used
• SSL support for Google searches from the Smart Search Field in Safari
• New preference to have Safari launch with previously open webpages

For detailed information on this update, please visit this website: http://support.apple.com/kb/HT5460
For information on the security content of this update, please visit: http://support.apple.com/kb/HT1222

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